This invention generally relates to breakable couplings used in medical applications wherein fluids are transported to and from patients, and more particularly relates to a xe2x80x9ctwist to separatexe2x80x9d breakable coupling which has a knit line at the intended point of fracture.
Within certain medical applications, it is desirable to withdraw fluids from or introduce fluids to a patient. One such application is peritoneal dialysis (e.g. continuous ambulatory peritoneal dialysis (CAPD) or automated peritoneal dialysis (APD)), wherein a cleansing fluid is introduced from a delivery line to a catheter which has been inserted into the abdomen of a patient. Waste is removed from the patient via the catheter. The delivery line which delivers the cleansing fluid to the patient is generally in the form of flexible tubing which transfers fluid to and from the catheter site. The catheter enters the peritoneal cavity, and a catheter connector is disposed between the tubing and the catheter. A releasable manual clamp is typically threaded onto the tubing to occlude the tubing as it is connected to the catheter through the catheter connector. Typically, a permanent manual clamp is also included to permanently occlude the tubing when the dialysis is completed so that the tubing can be disconnected from the catheter connector without any spilling of the drained fluids. A wide variety of tubing sets are known in the art and are used in a number of different applications.
Upon completion of the dialysis, it is necessary to disconnect the patient from the tubing set. This is normally accomplished by permanently occluding the delivery line by closing the permanent manual clamp, and then cutting the tubing on the side of the permanent manual clamp away from the patient. The permanent manual clamp thereby occludes the delivery line on the patient side in order to prevent any spilling of the drained fluid. After the tubing is cut, a clamp on the catheter is used to occlude the catheter, and the stub of the tubing is removed from the catheter. When dialysis is to be repeated, a new tube is connected to the catheter, the catheter clamp is loosened, and the process is repeated.
The cutting of the delivery line is normally accomplished with a pair of scissors or a knife. This, of course, requires that a pair of scissors or knife be available. Moreover, because peritoneal dialysis therapy is purposely designed so that it can be administered by the patient without the help of a nurse or other person, such as at home or at work, the pair of scissors or knife must be located so that the patient can reach them while still connected to the tubing set.
Another problem with a system in which the delivery line is cut with a knife or a pair of scissors is that there is no indicator on the delivery line of where it should be cut. A frequent problem, therefore, is that the patient accidentally cuts the delivery line on the patient side of the clamp, thereby spilling drain fluid. Even worse, the patient sometimes accidentally cuts the catheter rather than the tubing, thereby requiring the removal of the damaged catheter and the insertion of a new catheter.
Breakable tubing couplings which provide a pre-defined point of fracture (i.e. a pre-defined break zone), and provide that fracture can be accomplished without having to use a knife or a pair of scissors, are known in the prior art. Typically, such breakable tubing couplings provide as such viz-a-viz a molded-in circumferential groove which serves as the intended point of fracture. Two such breakable tubing couplings are disclosed in U.S. Pat. Nos. 5,221,267 and 5,423,768.
It is well known that a groove or notch can serve to concentrate stress upon parts that are loaded in a manner that places the notched or grooved side of the part under tension. In an injection molded part, plastic resin within such a groove may have the same or, depending upon the resin, even greater tensile strength on a pounds per square inch (p.s.i.) basis when compared to the parent material. By virtue of the overall lower cross sectional area of material present at the groove as compared to the rest of the part, any applied bending forces are concentrated at the groove which allows the part to predictably break along the groove in the same manner as a notch. Local restrictions within an injection mold that entirely traverse the direction of flow of injected plastic resin can cause the resin""s polymer chains to begin to align along the axis of flow resulting in material that is xe2x80x9clinearxe2x80x9d. Linear plastics have greater tensile strength than the normal random polymer chain orientation as a result of having more of the polymer chains commonly aligned (this phenomenon is employed to advantage in forming integral xe2x80x9cliving hingesxe2x80x9d in plastic parts and is often used in extrusion processes for greater longitudinal tensile strength and durability).
Generally, prior art couplings are designed such that a user must grip the coupling on both sides of the intended point of fracture (i.e. on both sides of the circumferential groove), and apply bending forces to effect the break at the groove. Due to the fact that the plastic resin within the groove may have the same or even greater tensile strength compared to the parent material, breakable couplings which provide a groove as the intended point of fracture can require relatively significant bending forces to effect the break. This is disadvantageous, and is especially disadvantageous in a case where a patient is weak and is attempting to break the coupling at home. Generally, prior art breakable couplings which provide a groove as the intended point of fracture do not include any type of break assistance structure, such as finger grips.
Additionally, by relying upon bending to effect the fracture, prior art breakable couplings generally break apart rapidly when broken. The instantaneous release of the user""s bending energy results in the broken ends of the coupling accelerating apart at the moment of break. This acceleration of the ends may serve to fling or spray fluid (perhaps contaminated fluid) into the surrounding environment, which is undesirable regardless of the setting (i.e. a clinical setting, a patient""s home or work, etc.).
An object of an embodiment of the present invention is to provide a frangible hose connector which includes a knit line at the intended point of fracture.
Another object of an embodiment of the present invention is to provide a frangible hose connector which provides a pre-defined point of fracture that does not include a circumferential groove or notch.
Still another object of an embodiment of the present invention is to provide a frangible hose connector which includes break assistance structure, such as finger grip levers.
Still yet another object of an embodiment of the present invention is to provide a frangible hose connector which is configured to be fractured via a xe2x80x9ctwist to separatexe2x80x9d arrangement (i.e. viz-a-viz a twisting or torsion force), as opposed to a bending force.
Yet still another object of an embodiment of the present invention is to provide a frangible hose connector which has a lower tensile strength at an intended point of fracture than that of the parent material, thereby providing that the connector is relatively easy to fracture.
Another object of an embodiment of the present invention is to provide a frangible hose connector which is easy to break apart and is designed to break in a manner wherein fluid does not tend to fling or spray into the surrounding environment.
Briefly, and in accordance with at least one of the foregoing objects, an embodiment of the present invention provides a frangible hose connector that includes a body having a first end and a second end generally opposite the first end. A throughbore extends through the body, and a knit line is provided in the body, between the first and second ends. The knit line defines an intended point of fracture of the body.
Preferably, the connector is formed of plastic and the knit line is created during a plastic injection molded process, wherein the flow of molten plastic within the mold cavity is controlled during the molding process in a manner which creates the knit line. At least one mold cavity fill point is provided on each side of the intended point of fracture, and when the plastic is injected, two mold fronts meet to define the knit line. To provide a mold cavity fill point on each side of the intended point of fracture, separate gates can be employed. Alternatively, two divided flow fronts from a single gate can be employed. Regardless, preferably the mold cavity includes stepped features which cause the mold fronts to xe2x80x9csquare-upxe2x80x9d with each other as they converge at the intended point of fracture, thereby providing a knit line which is generally regular. Preferably, such a process provides a knit line which has a lower tensile strength than that of the parent material. Ideally, the mold fronts do not exchange polymer chains and only abut very tightly, thereby producing a part which is effectively comprised of two weakly bonded pieces, bonded at the intended point of fracture.